Water voles are being returned to a lake in the Yorkshire Dales in what is thought to be the highest reintroduction project for the endangered mammal in Britain.
About 100 of the rodents are being returned to Malham Tarn by the National Trust, which says it will be the first time the mammals have been seen there in 50 years.
The tarn is 1.272ft (377m) above sea level and is England's highest freshwater lake.
National Trust ecologists believe Malham Tarn's water voles were wiped out in the 1960s by mink, which escaped from nearby fur farms.
The water vole - which is still best known as the inspiration for the character Ratty in Kenneth Grahame's Wind In The Willows - is Britain's fastest declining wild mammal.
The trust owns Malham Tarn and says it is reintroducing the mammals as part of a major new vision for land management in the Yorkshire Dales National Park, where it manages 8,000 hectares of moorland, farmland and woods.
It said they will play an important role in providing space for rare mosses and liverworts which need patches of open habitat to grow and will be a food source for struggling predators like barn owls and otters.
Roisin Black, National Trust ranger at Malham Tarn, said: "In the rest of Europe, water voles are common. In Britain, the creatures are incredibly rare.
"We know water voles have thrived at Malham Tarn in the past and, thanks to work by the National Trust, the habitat here is perfect for water voles again.
"By reintroducing water voles to the Tarn, we hope to give these rare animals the chance to recolonise the streams in the high Yorkshire Dales."
The animals, which have been bred in captivity, will be released in the fen area of the tarn this year, with a further 100 voles due to be released in June 2017.
Peter Welsh, ecologist for the National Trust in the Yorkshire Dales, said: "Water voles once played an important part in the ecosystem at Malham Tarn.
"Reintroducing them to the tarn is just one of the ways we are working alongside our farmers and other partners to restore wildlife and natural processes in the Yorkshire Dales landscapes we care for."
Here are some facts from the National Trust about water voles:
:: They measure around 12in (31cm) in length (8in/20cm body, 4in/11cm tail) and weigh between 200g and 350g - about the same as a half-size tin of baked beans.
:: They live in burrows dug into banks along slow-moving rivers, streams, ditches and in wetlands.
:: They are predominantly herbivores, eating grass and other waterside vegetation.
:: A water vole will consume around 80% of its body weight in food every day.
:: Water voles love sweet treats. During the release at Malham Tarn the water voles will be fed apples and carrots. Rangers will prepare 50 apples each day as treats for the voles.
:: Depending upon sex and age, water voles have a territory of between 30 and 300 metres.
:: Water voles will produce between two and five litters every year, with each litter comprising up to eight pups.
:: Young voles are weaned at two weeks of age.
:: Water voles live for up to three years in captivity but in the wild they can make an easy meal for predators and have a life expectancy of five months.
:: Water voles are the UK's fastest declining wild mammal. They have disappeared from about 90% of the rivers and streams where they were once common.
:: Threats to water voles include predation by mink, industrialisation of agriculture, housing development on floodplains and pollution of waterways.